An electrophoresis apparatus has been conventionally used for analysis of a trace amount of protein, nucleic acid, or the like. A typical example of such an electrophoresis apparatus includes a capillary electrophoresis apparatus using a capillary tube. However, such an apparatus using a capillary tube requires complicated handling. Therefore, in order to facilitate the handling of the apparatus and to achieve an increase in the speed of analysis and a reduction in the size of the apparatus, various substrates for analysis such as a microchip formed by providing a capillary in a substrate and a capillary plate formed by providing a plurality of capillaries in one plate have been proposed and used (see Patent Documents 1 and 2).
In such a substrate for analysis, a capillary formed therein is used as a separation channel for electrophoresis or a column for liquid chromatography. The capillary has both ends open at the surface of the substrate, and an opening provided at one of the ends of the capillary serves as a reservoir for injecting a sample.
Electrophoresis using a substrate for analysis involves a sample introduction step as pretreatment for analysis. As one pretreatment method, an electrokinetic injection method can be mentioned. According to this method, a sample is injected into a reservoir in a state where a capillary is filled with a separation medium, a voltage is then applied through an electrode to introduce the sample into the capillary, the reservoir is then washed and filled with a buffer solution, and a voltage is then applied through an electrode to carry out electrophoretic analysis of the sample.
Patent Document 1: Japanese Patent Application Laid-open No. 2002-310990
Patent Document 2: Japanese Patent Application Laid-open No. 2003-166975